Thermoplastic elastomers are a class of useful materials that have a unique combination of properties. The materials, for instance, can be formulated so as to be flexible and tough, while having elastic characteristics. Of particular advantage, the materials can also be melt processed due to their thermoplastic nature. Furthermore, unlike their cross-linked rubber counterparts, thermoplastic elastomers can be recycled and reprocessed.
Thermoplastic elastomers are used in numerous applications. The materials, for instance, may be molded to form a particular part or product or may comprise a component in a product. In addition, these materials may also be over-molded allowing for an additional layer to be formed on an initially molded part. Due to their flexible and elastic nature, thermoplastic elastomers are commonly used in applications where the material constantly undergoes deformation or otherwise contacts other moving parts.
Although thermoplastic elastomers can be used in numerous applications, problems have been experienced in the past in processing the elastomers. For instance, some thermoplastic elastomers have relatively high viscosities that cause problems in filling mold cavities. Other thermoplastic elastomers may have low melt strength which causes issues during extrusion and blow molding. In addition, some thermoplastic elastomers are not only expensive to produce, but also may darken or yellow in color over time. In addition, weathering may also affect the mechanical and thermal properties of the thermoplastic elastomers over time.
In order to correct some of the above noted problems, thermoplastic elastomers have been combined with other polymers. For example, mixtures of thermoplastic elastomers and an ethylene vinyl acetate copolymer have been proposed. In fact, the combination of a thermoplastic polyester elastomer and an ethylene vinyl acetate copolymer has shown to produce a polymer composition having many useful properties. Further improvements, however, are still needed.
For instance, oil resistance can be an important characteristic or property for a thermoplastic elastomer composition that is used to produce automotive parts, machine parts, and articles constantly in touch with the human body, such as handles, knobs and grips. Repeated contact with oils, for instance, can cause some elastomers to not only discolor, but also to experience a loss in mechanical properties. For example, human skin secretes sebum, which is known to attack polymer chains and reduce molecular weight. Also, artificial sebum may be applied to skin and is made of natural and artificial chemicals such as unsaturated and saturated fatty acids (e.g. oleic acid, stearic acid, palmitic acid) triglyceride oils etc.
Although adding an ethylene vinyl acetate copolymer to an elastomer can improve the oil resistance properties of the elastomer, the resulting composition is still susceptible to degradation when repeatedly contacted with oils in some applications. Thus, a need still remains for an elastomeric composition that has improved oil resistance.
A need also exists for molded articles made from an elastomer, such as a polyester elastomer, that display a metallic finish in addition to having improved oil resistance.